Cobalt sputtering target and sputter deposition of Co thin films for cobalt silicide metallization

CoSi2 is considered an alternative to TiSi2 for use as a contact in ultrala rge scale integration due to its low resistivity, excellent chemical stabil ity and lower formation temperature. Sputter deposition of Co thin films is one of the crucial steps in the cobalt salicide (a self-aligned silicide) process. One major problem with sputter deposition of Co thin films is that Co is a ferromagnetic material and is difficult to sputter. The de magneti c field transmitted through a ferromagnetic material from one side to anoth er is called the pass-through flux (PTF). In this study, the effects of tar get PTF:and. sputtering process parameters such as Ar pressure and sputteri ng power on the sputter process were studied. Co targets with PTF% of 65% ( high PTF), 53% (medium PTF) and 32% (low PTF) were sputter tested. The sput ter deposition rate, I-V characteristics, film sheet resistance and film un iformity were measured under various sputter conditions. The study indicate d that, in magnetron sputtering of Co, a high magnetic flux intensity could be obtained by using a high PTF target that allowed maximum magnetic flux to permeate through the target. The I-V characteristics of different PTF ta rgets followed the typical I=KVn relationship of dc planar magnetron sputte ring. The exponents in the equation, n increased with increasing target PTF %, indicating the sputtering imp;dance decreased with increasing target PTF %. The target with the highest PTF% demonstrated the best performance and f ilm uniformity. Rapid thermal processing (RTP) was carried out to form coba lt silicides at temperatures between 300 and 850 degrees C in Ar atmosphere for various times. The sheet resistance of the Co and cobalt silicide film s produced was monitored by a four-point probe before and after the RTP. Th e sheet resistance decreased significantly after annealing at 600 and 700 d egrees C due to formation of CoSi2, which has lower resistivity; The signif icant increase in sheet resistance after annealing at 400 and 500 degrees C was attributed to formation of the CoSi phase. For the 16 nm thick Co film , a sheet resistance of 3.2 Omega/sq was obtained after RTP at 600 arid 700 degrees C. (C) 1999 American Vacuum Society. [S0734-2101(99)12804-5].